1. Field of the Invention
The present invention relates to a random pitch impeller for a fuel pump, and more particularly, to a random pitch impeller for a fuel pump, in which blades of the impeller used for the fuel pump are arranged at random pitches, thereby reducing high-frequency noise generated by rotation of the impeller, and minimizing pulsation noise attributable to random intervals.
2. Description of the Related Art
There have been known various apparatuses for drawing and/or discharging fluid, one of which is a fuel pump. This fuel pump is used in the fuel supply system of the internal combustion engine and draws or discharges fluid, particularly fuel, by means of rotation of a rotating member such as an impeller formed on a disc and having blades on the outer circumference thereof.
As illustrated in FIG. 1, the fuel pump includes a pump housing 102 having upper and lower housing parts, a disc-shaped impeller 101 rotatably installed in the pump housing 102, and a drive motor 103 rotating the impeller 101.
Generally, the impeller of this fuel pump has numerous blades installed on the outer circumference thereof at uniform pitches, i.e. at equal intervals. Thus, when the rotating member rotates, each blade of the impeller passes through a partition, which is installed on the housing holding the rotating member, at constant time intervals. At this time, the partition is located adjacent to the blade between inlet and outlet of the fuel. For this reason, a peak of sound pressure (i.e. noise) is created within a certain frequency band, i.e. a so-called blade passing frequency (BPF) band, corresponding to the number of blades (or the revolutions per minute (rpm) of the rotating member).
In order to solve this problem, Japanese Patent Publication No. Hei 11(1999)-50990 discloses a fluid drawing and discharging apparatus, in which the intervals between the blades are disposed in a random manner, namely in an irregular manner. The fluid drawing and discharging apparatus disclosed in the patent document encounters a phenomenon that the blades lean to one side as illustrated in FIG. 2 because the blades are randomly disposed.
Further, as illustrated in FIG. 3, since the time intervals at which each blade passes through the partition adjacent to the blade are constant without a difference, the sound pressure peak, a frequency of which is n times as high as a rotation-order frequency of the rotating member, occurs, or noise is increased within the frequency band of the sound pressure peak by resonance according to circumstances.
In order to overcome this drawback, Korean Patent Application Publication No. 1999-23306 discloses a fluid drawing and discharging apparatus, in which the sum “Sm” of angles of blades satisfies the expression, (360/k)−10≦Sm≦(360/k)+10(k=2, 3, 4), such that the average of incremental angles in a specific section is similar to a grand average, thereby reducing noise.
However, these fluid drawing and discharging apparatuses control the blade arrangement on the basis of a random number, so that prediction and control of the blade arrangement are impossible.